1. Field of the Invention
The present invention relates to a system and method for determining a communications schedule (also referred to as a communications link structure) for relay nodes of a wireless relay network.
2. Description of the Prior Art
Within a wireless network, there will typically be a plurality of nodes that need to communicate with each other, and wireless communications links are established between the various nodes to support such communications. Considering a wireless telecommunications network, for a downlink communication path a transmitting node (for example a base station (BS)) may need to communicate with a plurality of recipient nodes (such as mobile stations (MSs)/items of end user equipment (UEs)). Similarly, for an uplink communication path multiple transmitting nodes (for example MSs/UEs) may need to communicate with a particular recipient node (for example a BS).
A common approach for establishing such communications links involves providing a direct communications link between a transmitting node and a recipient node, such an approach often been referred to as a single-hop implementation. Such an approach can work well when the various transmitting and recipient nodes are relatively closely spaced, but generally the throughput achievable by such arrangements rapidly decreases as the spacing between the transmitting and recipient nodes gets larger.
To alleviate such problems, it is known to provide one or more relay nodes within a wireless network to allow data to be propagated via wireless links between a plurality of the relay nodes. The various relay nodes can be arranged so as to allow a transmitting node to communicate with a recipient node via a number of intervening nodes, the intervening nodes serving to propagate the data further along the relay structure formed by the relay nodes. A relay node that forms an intervening node may in some implementations also serve as a recipient node for some communications (for example within a downlink communication path) or as a transmitting node for some communications (for example within an uplink communication path). Through the use of such a relay network, transmitting and recipient nodes are able to communicate with each other even when they are separated by a distance which would otherwise preclude such communication, due for example to an unacceptable level of attenuation of the signal if a direct communication were attempted between the nodes.
In accordance with a typical form of relay network, one or more separate relays may be provided by the relay network, and a multi-hop nearest neighbour relaying approach is taken, where each relay node transmits data to the nearest relay node within the relay to which that relay node belongs. However, whilst such an approach enables data to be transmitted over much larger distances than the earlier-described single-hop approach, the capacity required by the various communications links varies significantly. For instance, considering the downlink example where a transmitting node serves as the source of various communications traffic to a plurality of recipient nodes, the first wireless communications link between that transmitting node and the nearest relay node in the relay must have capacity to carry all of the communications traffic output from the transmitting node and destined for a recipient node covered by the relay, irrespective of which particular recipient node it is destined for. In many implementations, it can be very difficult to provide the required capacity over such a communications link to ensure reliable communication between all transmitting node/recipient node pairs.
Accordingly, it would be desirable to provide an improved mechanism for determining a communications schedule/communications link structure for routing data between a plurality of relay nodes forming a relay network.